1. Field of Use
This invention relates generally to automatic label applying apparatus which comprises a motor driven conveyor for advancing packages to a weighing scale and then to a label application station where a movable heated label applicator applies an appropriately printed label. In particular, the invention relates to such apparatus including means sensing if a package is present at the station, for sensing if a label is available for application and for preventing contact of the heated label applicator with the package and for stopping the conveyor after a short interval of time after a package arrives at the station but no label is in readiness to be applied.
2. Description of the Prior Art
U.S. Pat. Nos. 3,372,079; 3,605,986; 3,616,094; 3,264,161; and 3,751,321 disclose prior art apparatus, or parts thereof, which weigh a package and transmit the weight information to a label printer which then prints the weight and other data on a label. The printed label is then automatically transferred from a label issuing means by means of a vacuum transfer nozzle (usually heated) for application to the package. If packages are fed to the apparatus while the label issuing means has ceased to issue labels, there results an accumulation of unlabelled packages which need to be reprocessed through the machine. Absence of labels may, for example, be due to the fact that the label magazine has run out of labels or a label has jammed inside the printing mechanism or for some other reason. Furthermore, if the label applicator is heated and no label is disposed thereon, the package may be burned and damaged if the machine comes to rest with the label applicator in contact with the package.
U.S. Pat No. 3,751,321 discloses apparatus wherein a vacuum sensor is provided to sense the absence of a label on the vacuum transfer nozzle and to automatically stop the machine conveyor, thereby preventing continued advancement of packages to the label application station. A package sensor in the form of a photoresponsive device is located in the path of travel of the packages. The package sensor is actuated by a package moving to the label application station. The package sensor energizes a package sensing relay which conditions the circuit for subsequent operation. If a label is not transferred by the vacuum transfer nozzle, a vacuum sensor switch remains closed and its label sensing relay stays energized until a cam driven by the machine motor completes one revolution and actuates a limit switch to stop the conveyor motor. However, if a label is transferred, the increase in suction or lack of pressure in the vacuum line connected to the vacuum transfer nozzle causes the vacuum sensor switch to open and interrupt current flow to the coil of another relay which then permits the conveyor motor to continue to run even though the cam completes one cycle of operation and the limit switch is actuated. This apparatus employs a cam operated limit switch to stop the machine conveyor in the event that a package is present at the labelling station for an interval of time no label is in readiness to be applied during the interval. It is desirable, however, to avoid the use of a machine driven cam operating limit switch for this purpose for several reasons. For example, in such an arrangement, the length of the time interval which can exist before the conveyor stops needs to be varied to accommodate packages of different size and to suit the speed at which the apparatus is set to operate. It is difficult, time consuming and relatively costly with such a cam operated switch arrangement to vary the time interval because it is necessary to change cam sizes or cam types or alter the switch settings.